Chapter 2 · Magnetic Effects of Electric Current and Measuring Instruments: practice questions

Two long parallel straight wires carry electric currents in the same direction. The two wires:

• Aattract each other
• Bexert no force on each other
• Crotate about a common axis
• Drepel each other

A straight current‑carrying wire is placed parallel to the lines of a uniform magnetic field. The magnetic force acting on the wire is...

• Azero
• Bequal to BI
• Chalf its maximum value
• Dmaximum and equals BIL

In a moving-coil galvanometer the magnetic field is made radial by using a cylindrical soft-iron core between concave pole pieces. This is done so that:

• Athe current through the coil is doubled
• Bthe coil never rotates
• Cthe angle of deflection is directly proportional to the current for every position of the coil
• Dthe magnetic torque on the coil becomes zero

A circular coil of 50 turns and radius 5 cm carries a current of 2 A. The magnetic flux density at its centre equals... (μ₀ = 4π×10⁻⁷ T·m/A)

• A6.28×10⁻⁴ T
• B1.26×10⁻⁴ T
• C1.26×10⁻³ T
• D2.51×10⁻³ T

A horizontal straight wire carries a current directed towards the north and is placed in a uniform magnetic field directed vertically upwards. By Fleming's left‑hand rule, the magnetic force on the wire is directed towards the...

• Avertically downwards
• Beast
• Cwest
• Dvertically upwards

A long straight wire lies in the plane of the page and carries a conventional current directed to the right. The magnetic flux density at a point directly above the wire (in the plane of the page) is directed...

• Ato the left
• Bto the right
• Cinto the page
• Dout of the page

In a direct-current (DC) motor, the function of the split-ring commutator is to:

• Areverse the direction of the current in the coil every half revolution so that the coil keeps rotating in the same sense
• Bincrease the current supplied to the coil
• Cconvert alternating current into direct current before it enters the coil
• Dproduce a radial magnetic field around the coil

A proton of mass 1.6 × 10⁻²⁷ kg and charge 1.6 × 10⁻¹⁹ C moves with a speed of 2 × 10⁵ m/s perpendicular to a uniform magnetic field of flux density 0.5 T. The radius of its circular path equals:

• A4 × 10⁻³ m
• B2 × 10⁻³ m
• C4 × 10⁻² m
• D8 × 10⁻³ m

A wire of fixed length is first wound into a single circular turn of radius (r) carrying a current (I), giving a flux density (B₁) at its centre. The same wire is then wound into two turns carrying the same current, giving (B₂) at its centre. The ratio B₂/B₁ equals...

• A1/4
• B2/1
• C4/1
• D1/2

The magnetic flux density at a perpendicular distance of 2 cm from a long straight wire is 5×10⁻⁵ T. The current passing through the wire equals... (μ₀ = 4π×10⁻⁷ T·m/A)

• A0.5 A
• B2.5 A
• C5 A
• D10 A